ADDED: file_modification_time/2, obtaining a time stamp.

This addresses a remaining aspect of #511.

src/lib/files.pl

@@ -53,10 +53,12 @@
                   delete_file/1,
                   make_directory/1,
                   working_directory/2,
-                  path_canonical/2]).
+                  path_canonical/2,
+                  file_modification_time/2]).
 
 :- use_module(library(error)).
 :- use_module(library(lists)).
+:- use_module(library(charsio)).
 
 list_of_chars(Cs) :-
         must_be(list, Cs),
@@ -119,3 +121,12 @@ path_canonical(Ps, Cs) :-
         maplist(must_be(character), Ps),
         can_be(list, Cs),
         '$path_canonical'(Ps, Cs).
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   T is the modification time of File.
+   T is a time stamp, suitable for use in format_time//2 in library(time).
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+file_modification_time(File, T) :-
+        '$file_modification_time'(File, T0),
+        read_term_from_chars(T0, T).